Question: Solve for $r$. $-13 =\dfrac r9+8$ $r =$
Let's subtract and then multiply to get $r$ by itself. $\begin{aligned} -13 &=\dfrac r9+8 \\ \\ -13{-8} &= \dfrac r9+8{-8}~~~~~{\text{subtract }8} \text{ from each side}\\ \\ -13{-8}&=\dfrac r9+\cancel{ 8} {{-}\cancel{{8}}}\\ \\ -13{-8}&=\dfrac r9\end{aligned}$ $\begin{aligned}-21 &= \dfrac r9 \\ \\ {-21}\cdot{{9}} &= \dfrac{r}9\cdot{{9}} ~~~~~~~\text{multiply each side by } {9} \text{ to get } r \text{ by itself }\\ \\ -21\cdot{{9}}&=\dfrac r{\cancel{9}}\cdot{\cancel{{9}}} \\ \\ {-21}\cdot{{9}}&=r \end{aligned}$ The answer: $r={-189}~~~~~~~~$ [Let's check our work!]